1. Field of the Invention
The present invention relates, in general, to a brake traction control system capable of preventing a wheel slip on a road surface, and, more particularly, to a brake traction control valve having a relief function, which spontaneously opens a hydraulic line to prevent an excessive increase in pressure of brake oil pressurized by a hydraulic pump when traction control is performed.
2. Description of the Related Art
In general, brake traction control is a technology applied to an Anti-lock Brake System (ABS). A traction control system spontaneously detects a wheel slip and brakes an automobile even when a driver does not depress a brake pedal, thus preventing a further wheel slip.
A hydraulic circuit to which the brake traction control system is applied, as shown in FIG. 1, includes a Normal Open (NO) valve 3 placed on a hydraulic line connected from a master cylinder 1 to wheel cylinders 2, a Normal Close (NC) valve 4 placed on a return hydraulic line from the wheel cylinders 2, a hydraulic pump 5 designed to generate a braking pressure by re-pressuring brake oil returning from the wheel cylinders 2, a low-pressure accumulator 6 and a high-pressure accumulator 7 placed upstream and downstream of the hydraulic pump 5 to accumulate pressures of circulated brake oil, respectively, and an Electronic Control Unit (ECU; not shown).
The hydraulic circuit is also used to perform brake traction control, and further includes a first bypass hydraulic line 8a connecting a hydraulic line connected to an outlet side of the master cylinder 1 with a hydraulic line connected to an inlet side of the hydraulic pump 5, a reciprocating hydraulic valve 8 placed on the first bypass hydraulic line 8a to be normally opened and be dosed when a driver depresses a brake pedal 11, a traction control valve 9 placed on a hydraulic line connecting the outlet side of the master cylinder 1 with an outlet side of the high-pressure accumulator 7 to be normally opened, and a relief valve 10 placed on a second bypass hydraulic line 10a connecting the outlet side of the high-pressure accumulator 7 with the outlet side of the master cylinder 1.
In the conventional brake traction control system, when a wheel slip is detected during a start of an automobile, the hydraulic pump 5 is operated under the control of the ECU and, thus, a braking pressure is applied to the wheel cylinders 2. At this time, the traction control valve 9 and the NC valve 4 are kept dosed, so that brake oil located on the outlet side of the master cylinder 1 is drawn into the hydraulic pump 5 through the reciprocating hydraulic valve 8, and the hydraulic pump 5 implements braking of the automobile by pressurizing the drawn brake oil. In the above-described process, when braking pressure formed on the outlet side of the hydraulic pump 5 is excessively high, the relief valve 10 is opened and brake oil flows toward the master cylinder 1 through the second bypass hydraulic line 10a, thus maintaining appropriate braking pressure.
However, the conventional brake traction control system is disadvantageous in that it is complicated and voluminous because it must be provided with the second bypass hydraulic line 10a and the relief valve 10 to prevent an excessive increase in pressure on the outlet side of the hydraulic pump 5.